US3606150A

US3606150A - Fluid heat apparatus

Info

Publication number: US3606150A
Application number: US847939A
Authority: US
Inventors: Jozef Rosiek
Original assignee: Potterton International Ltd
Current assignee: Potterton International Ltd
Priority date: 1968-08-15
Filing date: 1969-08-06
Publication date: 1971-09-20
Anticipated expiration: 1988-09-20
Also published as: DE1941530A1; FR2015730A1

Abstract

THE INVENTION PROVIDES A GAS-FIRED WATER HEATER COMPRISING A BURNER UNIT INCLUDING A MAIN BURNER AND A PILOT BURNER, A COMBUSTION CHAMBER AND A HEAT-EXCHANGER ASSEMBLY SEALED BY A CASING, TWO CONDUITS FOR ADMITTRING COMBUSTION AIR TO, AND EXHAUSTING CONBUSTION PRODUCTS FROM, THE COMBUSTION CHAMBER, A HORIZONTALLY DISPOSED BALANCED FLUE CONSTITUTED BY THE EXTREMITES OF SAID CONDUITS, AND AN EXTRACTION FAN INCORPORATED IN THE EXHAUST CONDUIT TO DRAW COMBUSTION PRODUCTS FROM THE CONBUSTION CHAMBER AND TO EXPEL SAID COMBUSTION PRODUCTS TO ATMOSPHERE THROUGH THE EXHAUST CONDUIT. PREFERABLY THE EXTRACTION FAN INCLUDES ELECTRICAL SWITCHING MEANS ADAPTED TO CONTROL THE COMBUSTION PRODUCTS EXTRCTION RATE OF THE FAN IN SUCH A MANNER THAT THE THROUGHPUT OF THE FAN REQUIRED FOR OPERATION OF THE MAIN BURNER IS REDUCED WHEN GAS IS SUPPLIED TO THE PILOT BURNER ONLY.

Description

p 0, 1971 J. ROSIEK 3,606,150

7 FLUID HEAT APPARATUS Filed Aug. 6, 1969 2 Sheets-Sheet l MM BY 1M1 wyumgm Sept. 2 0, 1971 Y os g 3,506,150

mun HEAT APPARATUS Filed Aug. 6. 1969 2 Sheets-Sheet W .BYMMJ ZZM M United States Patent Office 3,606,150 Patented Sept. 20, 1971 3,606,150 FLUID HEAT APPARATUS Jozef Rosiek, Surhiton, Surrey, England, asslgnor to Potterton International Limited, London, England Filed Aug. 6, 1969, Ser. No. 847,939 Claims priority, application Great Britain, Aug. 15, 1968, 39,031/68; May 2, 1969, 22,456/69 Int. Cl. F23n 1/02 I US. Cl. 23620 7 Claims ABSTRACT OF THE DISCLOSURE The invention provides a gas-fired water heater comprising a burner unit including a main burner and a pilot burner, a combustion chamber and a heat-exchanger assembly sealed by a casing, two conduits for admitting combustion air to, and exhausting combustion products from, the combustion chamber, a horizontially disposed balanced flue constituted by the extremities of said conduits, and an extraction fan incorporated in the exhaust conduit to draw combustion products from the combustion chamber and to expel said combustion products to atmosphere through the exhaust conduit. Preferably the extraction fan includes electrical switching means adapted to control the combustion products extraction rate of the fan in such a manner that the throughput of the fan required for operation of the main burner is reduced when gas is supplied to the pilot burner only.

This invention relates to a gas-fired water heater.

A known gas-fired water heater of the so-called balanced flue type essentially comprises a burner unit, combustion chamber and heat-exchanger assembly sealed by a casing with respect to the room in which the heater is installed and having two conduits for admitting com bustion air to, and exhausting the products of combustion from, the combustion chamber, the external extremities of the conduits being disposed externally of the room closely and parallelly to one another in a common terminal unit so as to provide automatic draught compensation in accordance with varying wind conditions.

For many domestic gas-fired water heaters, especially those of small modern dwellings, it is desirable that the Water heater should be of small overall dimensions to enable it to be sited in an unobtrusive manner on a kitchen wall or under a working surface, for example. One known such balanced-flue heater of the type described above achieves a high thermal output and compact dimensions by including a high efficiency heat-exchanger and electric fan means for forcing air into the combustion chamber. The advantage of such forced-draught heaters as compared with appliances that rely upon convected aid circulation is that the cross-sectional areas of the inlet and outlet conduits is reduced.

However the above-mentioned heater essentially entails the use of a slightly pressurised combustion chamber and it is possible for combustion ,(or fine) products to escape into the room if leakage occurs in the sealed cas ing which surrounds the combustion chamber. For example, if the casing is constructed of sheet metal, leakage can occur if not all of the panels are accurately formed so that their abutting edges do not produce the desired fluid-tight joint. Furthermore, leakage problems can arise if access openings to permit the servicing of internal components are not provided with efficient sealing gaskets. Yet again, if the casing is manufactured from steel sheet there is an inherent risk of corrosion which could perforate the casing thus to allow leakage into the room.

Furthermore when a heater of the type described above is used as a heat source for a domestic or similar waterheating installation it is essential that some form of thermostatic control is incorporated to provide a desired temperature. For example, if the heater is used purely for space heating purposes, a room air thermostat is usually provided to cut off the fuel supply to the burner when a predetermined air temperature is attained. Although it is possible to provide modulation control gradually to reduce the burning rate in accordance with the demand for heat, conditions can prevail when a minimum burning rate is greater than the heat loading, and in these conditions the thermostat causes the burner to be cut off. Similarly, when the heater is used in conjunction with a combined space-heating and consumable hot water system it is usual to provide a hot water tank tempera ture-sensing thermostat to restrict the primary hot water flow when a desired temperature is attained; thus the heat load is reduced and when the lower limit of modulation is exceeded the fuel supply to the burner is cut off. Thus, it will be seen that under certain heat-load conditions the burner will be frequently extinguished and relit, even though modulating controls may be employed.

It is usual practice in apparatus of the type described to connect the electric fan in an electrical circuit containing electrical means for controlling the supply of fuel to the main burner in such a manner that the fan operates only when the burner is alight. This electrical means conveniently comprises a solenoid-operated valve adapted to admit fuel there-through when it is energised and to cut off the supply of fuel when it is de-energised. The pilot burner, which is connected to the fuel supply at a point upstream of the solenoid valve, is capable of burning without artificial aid induction, and accordingly burns irrespective of operation of the electric fan.

We have found that the above described apparatus suffers from even further shortcomings. For example, an adequate amount of combustion air is not immediately available in the vicinity of the burner when the fuel valve is opened. The effect of this is to creat unreliable and noisy ignition. Furthermore, upon cutting off the fuel supply to the main burner the supply of combustion air is also abruptly cut off with the result that the system is not completely purged and thus certain combustion products remain within the heater. During the resultant cooling of the heater the said products inevitably condense and cause corrosion and formation of solids to take place within the casing and flue passageways of the heater. A similar detrimental effect is caused by the combustion products from the continuously burning pilot burner. The thermal output of the pilot burner is insuflicient to cause a satisfactory convected air flow through the inlet and exhaust conduits and consequently condensation takes place.

Particularly in the case of heaters having low-water capacity heat exchangers it is necessary to provide a safety temperature control means to safeguard against the attainment of abnormally high temperature conditions, for example, as may be created by failure of a water-circulating pump. This safety means comprises conveniently a thermally sensitive probe situated within the heat exchanger and capable of breaking the electrical circuit to the solenoid-operated gas valve when a water temperature of say 200 F. is attained. During stand-by conditions, when the main gas burner, the water-circulating pump and the fan are not in operation, it is possible for the pilot burner, which may typically be of 500 B.t.u./ hr. rating, to heat the small quantity of static water contained within the heat exchanger. The effect of this, under certain ambient conditions, is to actuate the above mentioned safety means and thus prevent future operathe above-mentioned leakage problem by providing a gasfired water heater in which the interior of the casing is, in use, subjected to a slight negative pressure with respect to ambient atmospheric air pressure.

It is a further object of the present invention to overcome the above-mentioned thermal and chemical problems by ensuring that air circulation continues within the relevant parts of the heater during periods when the pilot burner only is in operation.

The present invention provides a gas-fired water heater wherein the inlet and exhaust conduits extend horizontally or substantially horizontally therefrom and that an extraction fan is incorpororated in the exhaust conduit to draw combustion products from the combustion chamber and to expel said combustion products to atmosphere through the exhaust conduit.

The present invention further provides a gas-fired water heater as described above wherein the circuit containing the extraction fan includes electrical switching means adapted to control the volumetric air delivery rate of the fan in such a manner that the throughput of the fan required for operation of the main burner is reduced when gas is supplied to the pilot burner only.

A preferred gas-fired water heater in accordance with the present invention will now be described by way of example with reference to the accompanying diagrammatic drawings in which:

FIG. 1 is a vertical cross-sectional view of the heater, and

FIG. 2 depicts an electrical circuit diagram relating to the heater adapted for space heating purposes by means of a conventional small bore hot water circuit.

Referring 110W to FIG. 1, the Water heater comprises a rectangular box-like combustion chamber 1 having an open bottom, four vertical side panels 2 and a top panel 3 provided with a circular aperture 4 in its centre. Five bi-metallic finned heat-exchanger water tubes 5 are provided longitudinally across the combustion chamber and are connected together in series configuration by means of 180 U-shaped connection pieces (not shown) situated externally of the combustion chamber. Thus the flow of water passes five times through the appliance between inlet and outlet connections (not shown) secured to the left-hand bottom and top tubes 5 respectively. The burner unit comprises a main burner constituted, in simplified form, by a pair of burner rails 6 and 7 connected by a cross pipe 8 to a gas supply pipe 9 via a solenoid-operated gas valve 26, and a continuously burning pilot light 9a which is supplied from the gas supply at a point upstream of the valve 26 by means of a pipe 9b.

The combustion chamber, heat exchanger assembly and burner unit are enclosed within a sealed casing 10 which is spaced from the combustion chamber 1 so as to form vertical air ducts 11 and 12, and upper and

lower air chambers

13 and 14 respectively.

The casing is supported upon a pair of brackets (one of which is shown at 15) which are mounted within a room on the inside face of a cavity brick wall 16.

A pair of juxtapositioned horizontal rectangular conduits 17 and 18 are connected to the side of the casing and pass through an aperture formed in the wall 16 to a louvred terminal 19 as shown. The inlet conduit 17 is provided with upwardly directed louvres and serves to admit air into the upper air chamber 13, and the exhaust conduit 18 is provided with downwardly directed louvres and serves as an exhaust exit for the combustion gases from combustion chamber 1. The conduit 18 passes through the external wall of the casing 10 and communicates with the snail housing 20 of a centrifugal fan having a fan impeller 21 fast with the driving shaft of an electric motor 22. The eye intake of the impeller is positioned above the aperture 4 in the top panel 3 of the 4 combustion chamber. The electric motor is situated above the snail housing 20 by brackets (not shown) within the upper air chamber 13.

Mains current supply is applied to the heating apparatus at L and N on the left-hand side of the diagram. The LIVE supply L is fed through a fuse 23, the contacts of a clock programmer 24, the contacts of an air thermostat 25, to three electrical devices connected in parallel and thence back to the NEUTRAL supply N. The electrical devices are a solenoid-operated gas valve 26 for controlling the flow of gas to the main gas burner from the gas supply pipe 9, a centrifugal water pump 27 adapted to circulate hot water through the heatexchanger water tubes 28, and the coil windings 29 of a relay 30 having single-pole change-over contacts. Independently of the above circuit the windings 31 of the clock programmer 24 are connected to the NEUTRAL supply and additionally as the air thermostat 25 as illustrated is of the accelerated type, a resistance heater 32 is provided between the fixed contact of the same and the NEUTRAL supply.

The driving motor 22 of the air fan 21 is connected from the unswitched LIVE supply through the contacts of the relay 30, back to the NEUTRAL. It will be noted that the change-over contacts of the relay 30 connect to the air fan driving motor 22 via a 1500i) resistor 33 when the relay is de-energised, and alternatively by means of a direct wire 34 when it is energised. Thus it will be appreciated that when the air thermostat 25 is closed and the gas valve 26 and water pump 27 are operative, the relay will always be energised and consequently the air fan driving motor 22 will run at mains potential. Conversely, when the thermostat 25 is open and the gas valve 26 and water pump 27 are inoperative the air fan driving motor 22 will run at reduced speed. It will be apparent that this latter condition will prevail regardless of the operation of the programmer 24 or the air thermostat 25, with the result that a small air flow will always be maintained through the heater and the aforementioned problems are substantially overcome. I

The air-exhaust flow through the heater is indicated by a procession of arrows and is as follows. Assuming that the air thermostat 25 demands heat, gas supply is admitted to the burner rails 6 and 7 where it is ignited by the pilot light. Simultaneously with the admission of gas an electric current supply is connected to the relay 29, the effect of which is to direct current at mains potential to the air fan driving motor 2. The resulting operation of the fan expels the combustion products through the exhaust conduit 18 and combustion products are drawn into the eye of the impeller 21 through the aperture 4. The effect of this is to create negative pressure within the combustion chamber 1 and, to retain equilibrium, atmospheric air is drawn through the intake conduit 17 into the upper air chamber 13, downwardly through the vertical air ducts 11 and 12 and finally into the lower open bottom of the combustion chamber.

It will be appreciated that the fan driving motor will be cooled by incoming air and also that if any leaks should occur within the wall of the casing 10 atmospheric air from the room will enter into the case; thus it will be quite impossible for injurious products of combustion to leak into the room.

The circuit diagram must be regarded as a simple arrangement and in the case of dual-purpose heat supply functions, i.e. to provide for space heating and consumable hot-water requirements, additional circuitry and relays will be necessary; however, the essential integers formulating the invention will always be carried out in a manner similar to that described above. Furthermore it must be understood that the arrangement of the boiler as shown in FIG. 1 includes various conventional temperature control devices which are not specifically indicated or referred to. These comprise essentially a modulating type gas flow control valve disposed between the valve 26 and the main burner unit which is capable of being influenced in accordance with the water flow temperature, a pilot-light flame-failure safety device and also one or more excess temperature cut-out devices to safeguard the appliance against abnormal temperatures that may be created by component failure or water fiow obstruction, for example.

We have found that using a particular air fan as fitted to a water heater of 50,000 B.t.u./hr. thermal output, a 15,0000 resistor reduced the effective voltage, as applied to the fan, from a mains potential of 250 v. to 105 v. The effect of this was to reduce the throughput of the fan from 16 cu. ft./min. to 3 cu. ft./min. at rotational speeds of 2500 rpm. and 500 rpm. respectively. We have found that a throughput of 3 cu. ft./min. effectively prevents formation of condensation products and additionally has enhanced the reliability and quietness of operation of both the pilot and main burners.

Additionaly, because the air fan is continually in motion, it is capable of accelerating up to its full working speed in an extremely short time, whereas in the known arrangements this can occupy several minutes owing to inherent oil and other mechanical drag conditions associated with starting from cold.

What is claimed is:

1. A room-seal gas-fired water heater comprising a heater assembly including a housing defining a combustion chamber, an air inlet port in said housing, an exhaust outlet port in said housing spaced from said air inlet port, a burner unit including an intermittently operable main burner and a continuously burning pilot burner mounted in said combustion chamber, a tubular heat exchanger supported in said combustion chamber betwen said burner unit and said exhaust outlet port, a casing sealingly enclosing said heater assembly, first and second conduits extending horizontally from said casing and connected thereto to define an air inlet and exhaust outlet respectively, the outer end of each conduit being open to the atmosphere and the inner end of said first and second conduits being placed in communication with said air inlet port and said exhaust outlet port respectively, said outer ends being arranged closely and parallel together to provide a balanced-flue, rotary extraction fan means disposed in said second conduit for expelling combustion products drawn from said combustion chamber, electric motor means for rotating said extraction fan means and control means adapted to control the rate of flow of the combustion products from the apparatus so as to provide a first effective volumetric throughput when both the main and pilot burners are in operation, and

a normally operating second effective volumetric throughput less than the said first throughput for coperation with the pilot burner only.

2. Gas-fired water heating apparatus according to claim 1 wherein the said control means comprise an electrical switch adapted to selectively apply a first voltage to the electric motor means thereby to provide the said first throughput and a second voltage lower than the first voltage to the electric motor means to provide the said second throughput.

3. Gas-fired water heating apparatus as claimed in claim 2 wherein the said second voltage is derived by bringing a resistor in the circuit containing the said electric fan means.

4. Gas-fired water heating apparatus as claimed in claim 3 wherein the electrical switch comprises an electromagnetic relay having a coil which is energised simultaneously with a solenoid valve adapted when energised to admit gas to the main burner, the arrangement being such that when the relay coil is de-energised the said second voltage is applied to the electric fan means.

5. Gas fired water heating apparatus as claimed in claim 2 wherein the electrical switch comprises an electromagnetic relay having a coil which is energised simultaneously with a solenoid valve adapted when energised to admit gas to the main burner, the arrangement being such that when the relay coil is de-energised the said second voltage is applied to the electric fan means.

6. Gas-fired water heating apparatus according to claim 1 wherein said housing is disposed upright within said casing and said air inlet port is in the form of an open bottom on said housing, said exhaust outlet port being at the top of said housing, and said extraction fan means being aligned with said exhaust outlet port for receiving exhaust gases directly therefrom.

7. Gas-fired water heating apparatus according to claim 6 wherein said electric motor means are mounted in the path of air flowing through said air inlet.

References Cited UNITED STATES PATENTS 1,892,188 12/1932 Goodridge 236-16 2,246,566 6/1941 Ames et a1. 236-1AUX 2,635,813 4/1953 Schlenz 2361A 2,685,917 8/1954 Perry 236-1AX 2,958,377 11/1960 Laing 431-20X EDWARD J. MICHAEL, Primary Examiner